Abstract: The problems addressed by the present invention lies in providing a Group III nitride semiconductor substrate having a principal plane on which high-quality crystals can be grown and also providing a method for producing a Group III nitride semiconductor substrate capable of obtaining a crystal which has few stacking faults and in which stacking faults in directions parallel to the polar plane in particular have been greatly suppressed. The problem is solved by means of a Group III nitride semiconductor substrate having a plane other than a C plane as a principal plane, wherein a ratio (W1/W2) of a tilt angle distribution W1 of the principal plane in the direction of a line of intersection between the principal plane and the C plane to a tilt angle distribution W2 of the principal plane in a direction orthogonal to the line of intersection is less than 1.

Abstract: To produce a zinc oxide single crystal having a sufficiently low lithium concentration and a high crystallinity. A zinc oxide crystal is grown by hydrothermal synthesis method using a solution having a lithium concentration of 1 ppm or less (weight basis), while suppressing a fluctuation range of crystal growth temperature within 5° C. or at a temperature within the range of 300 to 370° C.

Abstract: A method for producing a nitride semiconductor, comprising controlling temperature and pressure in a autoclave containing a seed having a hexagonal crystal structure, a nitrogen element-containing solvent, a raw material substance containing a metal element of Group 13 of the Periodic Table, and a mineralizer so as to put said solvent into a supercritical state and/or a subcritical state and thereby ammonothermally grow a nitride semiconductor crystal on the surface of said seed, wherein the crystal growth rate in the m-axis direction on said seed is 1.5 times or more the crystal growth rate in the c-axis direction on said seed. By the method, a nitride semiconductor having a large-diameter C plane or a nitride semiconductor thick in the m-axis direction can be efficiently and simply produced.